Switching regulator, especially down converter, and switching/regulating method

ABSTRACT

A switching regulator, a step-down transformer in particular, is described, which has a switching device for generating a pulsed signal from an input signal as a function of a switching signal; a filtering device for filtering the pulsed signal and for outputting a smoothed output signal; a controllable amplifier device for generating the switching signal from a reference signal and an actual value signal obtained from the output signal via a feedback device as a function of a compensation signal; and a compensation-signal generating device ( 2 ) for generating the compensation signal ( 3 ) from the input signal ( 1 ). A switching regulation method is also described.

FIELD OF THE INVENTION

The present invention relates to a switching regulator, a step-downtransformer in particular, and a switching regulation method.

BACKGROUND INFORMATION

Switching regulators (SR), such as buck converters or step-downconverters, are used in many applications, for voltage matching andvoltage reduction in particular, in switched-mode power supplies, forexample.

In direct voltage supply circuits (power supply units) voltage isgenerally regulated by switching regulators via a timing voltage whichis applied to the control terminal of a power transistor. In thesimplest case, a timing frequency is derived by the regulator from thedirect voltage (controlled variable) to be regulated according to thedeviation from the reference variable (system deviation) and this timingfrequency times the power transistor and thus provides the regulatedoutput direct voltage, after low-pass filtering in particular.

The open loop gain of a switching regulator results essentially from again v_(R) of a control amplifier, gain V_(PWM) of a pulse-widthmodulator (PWM), ratio kist of an actual voltage divider of the outputvoltage in the feedback path, and the gain or damping H_(TPLC) of an LClow-pass filter at the output of a power amplifier of the switchingregulator: (V=kactual×v_(R)×V_(PWM)×H_(TPLC)).

Gain factor V_(PWM) of the pulse-width modulator results from thequotient between a battery voltage U_(BAT) (input signal) and a deltavoltage U_(osc) which is supplied to the pulse-width modulator(V_(PWM)=U_(BAT)/U_(osc)), delta voltage U_(osc) being 1.25 V_(SS), forexample.

Due to the great fluctuation range of battery voltage U_(BAT), ofapproximately 6 V to 40 V, and possibly even 60 V, which must be takeninto account, gain factor V_(PWM) of pulse-width modulator (PWM) has arelatively large dynamic range. As a result, the total gain varies by afactor of 10 (20 dB) due to the battery voltage variation range alone,which may result in stability problems of the overall control circuit,or in control and accuracy losses in the case of a reserve establishedon the basis of the maximum gain.

Changes in the battery voltage, in particular sudden changes, areidentified and subsequently adjusted in the feedback path of the controlcircuit of a switching regulator only with a relatively long delay time,which results in dynamic harmonics in the output voltage. Relevant forthe delay is the LC low-pass filter (H_(TPLC)) having a cut-offfrequency f_(gTP) of:f _(gTP)=(½π)×(1/(LC)^(0.5)).

A typical method for circumventing the above-named problems is presentedin M.R. BORGHI Smart Power ICs, Springer Verlag 1996. The amplitude ofdelta voltage U_(osc) supplied to the pulse-width modulator is regulatedas a function of the battery voltage U_(osc)=f(U_(BAT)), delta voltageU_(osc) being in the range between 200 mV and 2 V, for example. Onedisadvantage in the case of relatively small amplitudes of delta voltageU_(osc) in a timed system results due to the resolution inaccuracy,which is critical. In addition, amplitude feedforward compensation isrelatively complicated to implement.

Another typical method for circumventing the above-described problems isa pre-distortion of delta voltage U_(osc), the oscillator voltagesupplied to the pulse-width modulator being only quasi-delta shaped, anda linear section in the area of the tip of the delta having anexponential area where no feedforward effect is achieved, since theoscillator does not change its voltage amplitude, in particular not as afunction of battery voltage U_(BAT), and thus no direct compensationregulation occurs (see also MULLER RS, KAMINS TI (1986) Devices ForElectronics Integrated Circuit, John Wiley & Sons).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a switching regulator,in particular having feedforward compensation, and also a switchingregulation method having a gain which is essentially independent of aninput signal.

The present invention is based on the fact that gain VR of a controlamplifier is approximately proportional to the battery voltage.

The object of the present invention as recited in the preamble isachieved in particular by the fact that a compensation device controlsgain factor VR as a function of an input voltage, in particular afluctuating input voltage (U_(BAT), for example), in such a way that theoverall gain of the switching regulator remains essentially constantover battery voltage U_(BAT).

According to an advantageous refinement, an amplifier device has acomplex grounded resistor, in particular for adjusting a primary gainand/or frequency compensation.

According to another preferred refinement, a filtering device has alow-pass filter, in particular having an inductance and a capacitanceand a diode connected in parallel thereto.

According to another preferred embodiment, the oscillator signalsupplied to the pulse-width modulating device has a delta oscillatorvoltage.

According to another preferred refinement, a switching device has atransistor, a MOSFET in particular.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows the block diagram of a switching regulator, havingfeedforward compensation in particular, to elucidate an embodimentaccording to the present invention.

DETAILED DESCRIPTION

The FIGURE shows the block diagram of a switching regulator, havingfeedforward compensation in particular, to elucidate an embodimentaccording to the present invention. The FIGURE, an input signal 1, abattery voltage U_(BAT) in particular, is supplied to a compensationdevice 2, a feedforward compensation module (FFK) in particular, whichgenerates a compensation signal 3, a compensation current I_(FFK) inparticular, as a function of the amplitude of input signal 1.

An amplifier device 7, a control amplifier R_(V) or transconductanceamplifier in particular, receives compensation signal 3 and modifiesgain factor 6 V_(R) of amplifier device 7 according to compensationsignal 3. A complex resistor 8 is connected to amplifier device 7 and isessentially used for adjusting the primary gain of amplifier device 7and/or the frequency compensation. A reference signal 4, a referencevoltage U_(REF) in particular, and an actual value signal 5, an actualvoltage U_(actual) in particular, are also supplied to amplifier device7 to generate an amplifier signal 23.

An oscillator signal 9, a delta oscillator voltage U_(osc) inparticular, having any desired, essentially constant, amplitude is alsosupplied, as is amplifier signal 23, to a pulse-width modulating device11, a pulse-width modulator (PWM) in particular, which generates apulse-width modulated signal 22 amplified by a gain v_(PWM), which issupplied to an additional amplifier device 12 having gain v_(p). Aswitching signal 21 is generated in amplifier device 12, which isessentially used as a power adapter for actuating a switching device 13.

Switching device 13, a MOSFET power amplifier in particular, switchesthrough input signal 1 as a function of switching signal 21 to afiltering device 14 and as a result generates a pulsed signal 24, whichis smoothed in filtering device 14, which has a low-pass filter inparticular having a serial inductance 15 and a grounded capacitance 17connected downstream from inductance 15.

A freewheeling diode 16, which is used for protecting filtering device14 against voltage surges, among other things, is connected to ground inparallel to filtering device 14. Pulsed signal 24 is smoothed infiltering device 14 to yield output signal 18, a voltage in particular,which is supplied to amplifier device 7 (actual value signal 5) via aresistor network 19, a voltage divider 19 in particular having gain ordivision kist, and a feedback path 20. Gain v_(R) or transconductances_(R) of control amplifier 7 is corrected using battery voltage U_(BAT)(input signal 1) in such a way that the productv₁=(U_(BAT)/U_(osc))×v_(R) remains constant over the battery voltage.

Delta oscillator voltage U_(osc) may be selected arbitrarily, e.g.,U_(osc)=1.25 V. The loop gain in the control circuit of a buckconverter, which in first approximation is independent of the batteryvoltage according to the present invention, represents an implementationof a feedforward compensation, i.e., the control amplifier orpulse-width modulator responds to a sudden change in the battery voltageimmediately, without delay of the output-side low-pass filter.

The implementation of such a switching regulator using feedforwardcompensation is inexpensive and requires little space.

For gain v_(R) of control amplifier RV, the following applies:v _(R) =Z×[1/(R×k×U _(BAT))],where Z represents the complex resistance of a selectable externalresistor, having an ohmic and/or capacitive resistance in particular.The product of transconductance S_(R) and complex resistance Z is alsoequal to gain v_(R) of control amplifier RV, transconductance S_(R)being compensation current I_(FFK) divided by temperature voltage U_(T),and compensation current I_(FFK) being generatable from a ring-typecurrent source and satisfying the equation I_(FFK)=U_(c)/(R×k×U_(BAT)),R being the Tk0 resistance of the ring-type current source, and k beinga factor for adjusting gain v_(R). By combining the above equations andequation V_(PWM)=U_(BAT)/U_(osc), the product of the two gains V_(R) andV_(PWM)=v1 becomes v1=Z/(R×k×U_(osc)), which in first approximation isindependent of the battery voltage and in the event of battery voltagesurges corrects the gain dynamically, without delay time of the outputlow-pass filter, so that harmonics in output voltage V_(out) areprevented.

Although the present invention was described above with reference to apreferred exemplary embodiment, it is not limited thereto, but may bemodified in many ways.

Although in the example above the compensation device emits a currentsignal for controlling the gain factor of the amplifier device, anothersignal form (voltage signal, optical signal, etc.) is also conceivablehere or for the other mentioned signals. A different oscillator outputsignal form is also conceivable, as well as a modified filtering deviceor the omission of the additional amplifier device having gain factorv_(p).

The present invention is also not limited to the above-mentionedapplications.

1-16. (canceled)
 17. A switching regulator, comprising: a switchingdevice for generating a pulsed signal from an input signal as a functionof a switching signal; a filtering device for filtering the pulsedsignal and for outputting a smoothed output signal; a feedback device; acontrollable amplifier device for generating the switching signal from areference signal and an actual value signal obtained from the smoothedoutput signal via the feedback device as a function of a compensationsignal; and a compensation-signal generating device for generating thecompensation signal from the input signal.
 18. The switching regulatoras recited in claim 17, wherein: the switching regulator is a step-downtransformer.
 19. The switching regulator as recited in claim 17,wherein: the amplifier device includes a complex grounded resistor, foradjusting at least one of a primary gain and a frequency compensation.20. The switching regulator as recited in claim 17, wherein: thefiltering device includes a low-pass filter.
 21. The switching regulatoras recited in claim 20, wherein: the low-pass filter includes aninductance and a capacitance.
 22. The switching regulator as recited inclaim 17, further comprising: a diode is connected in parallel to thefiltering device in order to protect the filtering device.
 23. Theswitching regulator as recited in claim 17, further comprising: aresistor network including a voltage divider having essentially ohmicresistors and connected to the amplifier device via the feedback device.24. The switching regulator as recited in claim 17, wherein: thecontrollable amplifier device includes a pulse-width modulating devicefor generating a pulse-width modulated signal, corresponding to theswitching signal, from an oscillator signal and an amplifier signal. 25.The switching regulator as recited in claim 24, wherein: the oscillatorsignal has a delta voltage-shaped curve.
 26. The switching regulator asrecited in claim 17, wherein: the compensation signal is a currentsignal.
 27. The switching regulator as recited in claim 17, wherein: theswitching device includes a MOSFET transistor.
 28. The switchingregulator as recited in claim 17, wherein: the input signal includes aquasi-constant battery voltage.
 29. The switching regulator as recitedin claim 17, further comprising: a circuit arranged between thepulse-width modulating device and the switching device, the circuitincluding an additional amplifier device.
 30. A switching regulationmethod, comprising: generating a compensation signal from an inputsignal in a compensation-signal generating device; generating aswitching signal from a reference signal and an actual value signalobtained from the output signal via a feedback device as a function ofthe compensation signal in a controllable amplifier device; generating apulsed signal from the input signal as a function of the switchingsignal in a switching device; and filtering the pulsed signal in afiltering device and outputting a smoothed output signal.
 31. The methodas recited in claim 30, further comprising: generating an amplifiersignal via a complex resistor connected to the controllable amplifierdevice.
 32. The method as recited in claim 30, further comprising:supplying the smoothed output signal to the controllable amplifierdevice via a resistor network, including a voltage divider in particularprovided with ohmic resistors, and the feedback device.
 33. The methodas recited in claim 30, further comprising: generating a pulse-widthmodulated signal corresponding to the switching signal from anoscillator signal and the amplifier signal in the controllable amplifierdevice in a pulse-width modulating device.
 34. The method as recited inclaim 33, further comprising: amplifying the pulse-width modulatedsignal in an additional amplifier device before the switching device istriggered.